Low pressure warning system for pneumatic tires with RF tags and monitors for each tire

ABSTRACT

Method and apparatus ( 200 ) for monitoring vehicle tire pressure and warning the driver when a low tire inflation pressure condition occurs includes transponder tags ( 220   a    . . . 220   d   , 300, 300   a ) and associated sensors (e.g., pressure, temperature) for each tire and a monitor ( 230   a    . . . 230   d   , 400  disposed in close proximity to each tire ( 204   a    . . . 204   d ). In this case manner, a low-powered radio transmission can take place between each tire tag and an associated one of the monitors. Each monitor is connected to a vehicle data bus  206, 430 ) for communicating, preferably bi-directionally, with a computer ( 208 ), and a central display ( 212 ) provides visual (or audible) warnings to the operator of the vehicle. The system is simple in operation, economical to manufacture, easy to install, and highly reliable, and conforms to standards established for heavy vehicles, and can be used on passenger car applications as well.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to commonly-owned, PCT Patent Application No.PCT/US99/18610 filed Aug. 16, 1999.

TECHNICAL FIELD OF THE INVENTION

The invention relates generally to systems for measuring air pressure inpneumatic tires of vehicles and, more particularly, to systems includinga sensor and a transponder associated with each of the vehicle tires.

BACKGROUND OF THE INVENTION

Safe, efficient and economical operation of a motor vehicle depends, toa significant degree, on maintaining the correct air pressure in thetires of the motor vehicle. Failure to correct promptly forfaulty/abnormal (typically low) air.pressure may result in excessivetire wear, blow-outs, poor gasoline mileage and steering difficulties.

The need to monitor tire pressure is highlighted in the context of“run-flat” (driven deflated) tires, tires which are capable of beingused in a completely deflated condition. Such run-flat tires, asdisclosed for example in commonly-owned U.S. Pat. No. 5,368,082,incorporated in its entirety by reference herein, may incorporatereinforced sidewalls and mechanisms for securing the tire bead to therim to enable a driver to maintain control over the vehicle after acatastrophic pressure loss, and are evolving to the point where it isbecoming less and less noticeable to the driver that the tire has becomedeflated. The broad purpose behind using run-flat tires is to enable adriver of a vehicle to continue driving on a deflated pneumatic tire fora limited distance (e.g., 50 miles, or 80 kilometers) prior to gettingthe tire repaired, rather than stopping on the side of the road torepair the deflated tire. Hence, it is generally desirable to provide alow pressure warning system (LPWS) within the vehicle to alert (e.g.,via a light on the dashboard, or a buzzer) the driver to the loss of airin a pneumatic tire.

FIG. 1 illustrates a typical low pressure warning system (LPWS) 100 ofthe prior art installed on a motor vehicle 102 (shown in dashed lines)having four pneumatic tires 104 a . . . 104 d installed on fourrespective wheels (not shown). A transponder (“TAG”) 106 a . . . 106 dis associated with each of the tires 104 a . . . 104 d, respectively.

As used herein, a “transponder” is an electronic apparatus (device)capable of both receiving and transmitting radio frequency signals, andimpressing variable information (data) in a suitable format upon thetransmitted signal indicative of a measured condition (e.g., tirepressure) or conditions (e.g., tire pressure, temperature, revolutions),as well as optionally impressing fixed information (e.g., tire ID) onthe transmitted signal, as well as optionally responding to informationwhich may be present on a signal which is received by the transponder.

“Passive” transponders are transponders powered by the energy of asignal received from an external “interrogator” apparatus. “Active”transponders are transponders having their own power supply (e.g., abattery), and include active transponders which remain in a “sleep”mode, using minimal power, until “woken up” by a signal from aninterrogator.

The transponders 106 a . . . 106 d are suitably passive transponderswhich obtain their operating power from an RF signal which is providedby an on-board interrogator 108 which is mounted within the vehicle.

The interrogator 108 comprises an RF transmitter 112 (e.g., for poweringpassive transponders), an RF receiver 114, control logic 116 which mayinclude a microprocessor (μP), and a display device 118 such a visualdisplay and optionally including an audible alarm. Antennas (“ANT”) 110a . . . 110 d are disposed on the vehicle 102, preferably adjacent thetires 104 a . . . 104 d, respectively, such as in the wheel wells of thevehicle. The antennas 110 a . . . 110 d are suitably ferrite loopstickantennas.

The use of multiple vehicle antennas 110 a . . . 110 d, each at a fixedposition on the vehicle adjacent a respective tire 104 a . . . 104 d,such as in the wheel well, is well known, and is disclosed in U.S. Pat.Nos. 3,553,060; 3,810,090; 4,220,907; 4,319,220; and 5,774,047, all ofwhich are incorporated in their entirety by reference herein. In thismanner, close coupling can be effected between the tire transponders andthe vehicle antennas, thereby facilitating identifying which of theseveral wheels on a vehicle has a sensed low pressure condition.

In use, the interrogator 108 powers the transponders 106 a . . . 106 dwhich, in turn, transmit data indicative of a measured condition (e.g.,tire air pressure) back to the interrogator 108. In any such system, itis desirable to have efficient and effective coupling of signals betweenthe fixed antennas 110 a . . . 110 d (alternatively, onecentrally-located fixed antenna) and the moving (i.e., when the vehicleis in motion) transponders (each of which has its own antenna, notshown).

Low pressure warning systems for tires are generally well known, andrepresentative examples may be found in the following U.S. Patents, allof which are incorporated in their entirety by reference herein: U.S.Pat. No. 3,694,803 (Strenglein; 1972); U.S. Pat. No. 4,067,235(Markland, et al.; 1978); U.S. Pat. No. 4,334,215 (Frazier, et al.;1982); and U.S. Pat. No. 5,335,540 (Bowler, et al.; 1994).

An important feature of a viable low pressure warning system employingtransponders and an interrogator is providing effective coupling ofradio frequency (RF) signals between the transponders which may belocated inside of the pneumatic tires, and the interrogator which may belocated at some central location in the vehicle. An additional importantfeature of a viable low pressure warning system is providing anindication to the operator of the vehicle of the condition beingmonitored, for example, low tire pressure, correct tire pressure, etc.

For example, a straightforward approach is to have an RF transmitter andpressure sensor within each tire (e.g., affixed to the valve stemthereof). In order to save power, the transmitter may only transmit whenpressure drops below a threshold value. A single, centrally-locatedreceiver in the vehicle cab can detect the transmission, and cause anaudible signal to be sounded to alert the driver to the sensed lowpressure condition. In such a system, the RF transmissions from thetransmitters must be adequate to penetrate vehicle components to bedetected by the receiver. Generally, no hard wiring from the vicinity ofthe wheels to the receiver is required when utilizing such an RFcommunications link. When relying on robust RF coupling between theindividual transmitters (or transponders) and a central receiver (orinterrogator), techniques should be provided to prevent “false alarms”,such as a low tire pressure signal emitted by a transmitter of anothervehicle in close proximity to the vehicle in question. Additionally, itis sometimes desirable to be able to ascertain which of the several(e.g., four) tires on a given vehicle has a sensed low pressurecondition.

U.S. Pat. No. 3,533,060 (Garcia; 1970), incorporated in its entirety byreference herein, describes a pressure-responsive radio transmitter (13)disposed on each valve stem (21) of each tire (12) of a vehicle (11).

“Receiving antennas 16 are mounted in each of the wheel wells andconnected by appropriate leads to a receiver set 17 mounted on orattached to the dashboard of the vehicle 11 . . . the receiver set canbe of standard construction and include amplifying means to amplify thesignals picked up by the antennas 16 and means for indicating theoccurrence of such transmission, in the form of a buzzer, a bell, alight, or the like.” (column 2, lines 30-38)

U.S. Pat. No. 4,220,907 (Pappas, et al.; 1980), incorporated in itsentirety by reference herein, discloses a low tire pressure alarm systemfor vehicles such as trucks and cars. Each wheel is provided with atransmitter (200). A common receiver (300) has either a single receivingantenna, or multiple antennas, with each wheel having a separate antenna(302a . . . 302d) associated therewith. As disclosed therein at (column14, line 66 through column 15, line 3):

“If multiple antennas are provided, they would be optimally loops offairly large size, located near each wheel . . . however . . . a ferriteloopstick will do, and that smaller dimension of this arrangement makesfor a more convenient mounting package”

The possibility of two antennas at each wheel location is also discussedin this patent (column 15, lines 11-15). As shown in FIG. 15, fourantennas 302a . . . 302d may be selected, one at a time, by an analogswitch (304).

U.S. Pat. No. 5,541,574 (Lowe, et al., 1996), incorporated in itsentirety by reference herein, discloses (at FIG. 11 thereof):

“the electrical circuitry for a single exciter/reader [interrogator] 92is provided at a suitable location within the vehicle, and used tocommunicate with transponders (not shown) on each of the vehicle's wheelassemblies 2a-2d. The output of the exciter/reader 92 is time sharedbetween corresponding antenna coils 48a-48d adjacent each of the wheelsites. Only the antenna coils 48a-48d, and no electronics, are requiredat the localized wheel sites. This is facilitated by the extremesimplicity of the required signal protocol, and the large magnitude ofthe return signals. The exciter/reader 92 communicates with one tiretransponder at a time, deactivating a given transponder before moving onto the next. ” (column 7, lines 51-64)

U.S. Pat. No. 5,731,754 (Lee Jr., et al.; 1998), incorporated in itsentirety by reference herein, discloses an apparatus 10, comprising atransponder 18 and sensors, suitable for mounting within or on a vehicletire and which operates to sense and transmit various tire conditionparameters to a remote interrogation unit 80. As disclosed therein:

“A transponder and sensor apparatus with on-board power supply ismounted in or on a vehicle tire. A pressure sensor, a temperature sensorand a tire rotation sensor are mounted in a housing along with thetransponder, the power supply and an antenna. Upon receiving aninterrogation signal from a remote interrogator, the transponderactivates the sensors to sense tire pressure and temperature and thenbackscatter-modulates the radio frequency signal from the interrogatorwith the tire condition parameter data from the sensors to return thebackscatter modulated signal to the interrogator.”(Abstract)

The interrogator 80, as shown in FIG. 9 of U.S. Pat. No. 5,731,754,generates an interrogation signal which is transmitted by transmitter 84over an antenna 85. The interrogation signal is received by the remotelylocated transponders 18, which respond using a backscatter modulationtechnique. The backscatter-modulated signal from the transponder 18 ispassed by the antenna 85 to an input of a receiver 86, for decoding. Inthis manner,

“the tire condition parameter data from one or more apparatus 10 maythen be output from the interrogator 80 to an external host computer 90by suitable communication circuits including parallel, RS-232, RS-485and ETHERNET communication circuits.” (column 7, lines 55-59).

U.S. Pat. No. 5,790,016 (Konchin, et al.; 1998), incorporated in itsentirety by reference herein, discloses a tire pressure sensing system.A sensor-transducer (14) is mounted within each tire, and is essentiallya passive LC circuit with a pressure-sensitive switching element. Areceiver (20) is mounted in proximity to each tire, and comprisesinductors and an amplifier which together form an oscillator. The systemcontinuously monitors air pressure within each of the tires duringmotion of the motor vehicle though generation of an electromagneticcoupling between corresponding pairs of sensor-transducers and receiversduring an alignment that occurs between the transducers and couplersduring each rotation of the tire. An indicator interface (80) is locatedwithin the passenger compartment of the motor vehicle, such as on thedashboard, and displays the current status of each of the vehicle tires,such as with LEDs, to the motor vehicle operator. Each receiver isconnected to the indicator interface through wiring, or, alternatively,through a wireless communication link.

BRIEF DESCRIPTION (SUMMARY) OF THE INVENTION

It is an aspect of the present invention to provide method and apparatusfor monitoring an operating characteristic of a pneumatic tire, asdefined in one or more of the appended claims and, as such, having thecapability of being implemented in a manner to accomplish one or more ofthe subsidiary objects.

According to the invention, a Low Pressure Warning System (LPWS)comprises a “tag” associated with, and preferably disposed within, eachtire of a vehicle. At least one sensor is associated with each tag, suchas a pressure sensor. The tag is capable, in the least, of transmittingan RF signal modulated with information regarding measured air pressurewithin the tire, and may also include temperature data (in which case, atemperature sensor would also be associated with each tag). The RFsignals from the tire tags are low-power, short range signals and, foreach tag, are received by an associated monitor located in closeproximity to the respective tire tag, such as within the respectivewheel well of the vehicle. The monitor receives and demodulates the RFsignal from the associated tire tag, and impresses a data signalindicative of tire temperature (and, optionally, pressure) on a data buswithin the vehicle. An on-board vehicle computer is also connected tothe data bus, to receive and interpret the data. A display is alsoconnected to the data bus, to display the interpreted data, underdirection of the computer. Optionally, the tag is also capable ofreceiving information on an RF signal transmitted by the associatedmonitor. Such a signal is generated by the monitor in response to a datasignal impressed on the data bus by the computer. There is thus provideda method for measuring and monitoring tire pressure, and providing thisinformation to a driver of the vehicle, including warning the driverwhen a low tire pressure condition occurs.

An advantage of the LPWS of the present invention is that the samedesign can be used in all types of vehicles from passenger cars to heavyduty vehicles, including trailers. The LPWS can be offered as an optionby the vehicle manufacturer since it connects easily to (two wireplug-in connection, or 4 wires. Include power connections) andmultiplexes its data to existing RS-485 (or the like) vehicle databuses.

Another advantage of the LPWS of the present invention is that all tirepressure (and temperature) data can be displayed on the common vehicledisplay, thereby eliminating a requirement for a dedicated tireparameter display.

Another advantage of the LPWS of the present invention is that itfeatures a “short haul” (close proximity) RF link (between the tire tagand the antenna of the associated LPWS monitor) rather than a “longhaul” RF link. An advantage of “short haul” is a short unobstructedsignal path with resulting low power requirements and higherreliability, as well as other benefits of near field transmission.

Another advantage of the LPWS of the present invention is that, whenreceiving data the LPWS monitor removes the data from the RF signal andimpresses the data directly onto the data bus, thereby eliminating anyneed for RF energy to be routed over the vehicle wiring. Conversely,when transmitting, the LPWS monitor generates its own RF, againobviating any need for RF energy to be routed over the vehicle wiring.

Other objects, features and advantages of the invention will becomeapparent from the description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made in detail to preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. The drawings are intended to be illustrative, not limiting.Although the invention will be described in the context of thesepreferred embodiments, it should be understood that it is not intendedto limit the spirit and scope of the invention to these particularembodiments.

Elements of the figures are typically numbered as follows. The mostsignificant digits (hundreds) of the reference number corresponds to thefigure number. Elements of FIG. 1 are typically numbered in the range of100-199. Elements of FIG. 2 are typically numbered in the range of200-299. Similar elements throughout the drawings may be referred to bysimilar reference numerals. For example, the element 199 in a figure maybe similar, and possibly identical to the element 299 in an otherfigure. In some cases, similar (including identical) elements may bereferred to with similar numbers in a single drawing. For example, eachof a plurality of elements 199 may be referred to individually as 199 a,199 b, 199 c, etc. Such relationships, if any, between similar elementsin the same or different figures will become apparent throughout thespecification, including, if applicable, in the claims and abstract.

The structure, operation, and advantages of the present preferredembodiment of the invention will become further apparent uponconsideration of the following description taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a simplified block diagram of a low pressure warning system(LPWS), according to the prior art;

FIG. 2 is a schematic illustration of a multiplexed low pressure warningsystem (LPWS) installed on a vehicle, according to the invention;

FIG. 3 is a schematic illustration of an exemplary wheel station readerfor the LPWS system of FIG. 2, according to the invention;

FIG. 3A is a schematic illustration of an alternate embodiment of anexemplary wheel station reader for the LPWS system of FIG. 2, accordingto the invention; and

FIG. 4 is a schematic illustration of an exemplary electronic “tag”,located within each tire of the vehicle, for the LPWS system of FIG. 2,according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 illustrates an embodiment of the Low Pressure Warning System(LPWS) 200 of the present invention, installed on a vehicle 202 (shownin dashed lines), such as a typical passenger vehicle having fourpneumatic tires 204 a, 204 b, 204 c and 204 d installed on fourrespective wheels (not shown).

The vehicle 202 is preferably equipped with an RS-485 (or equivalent)multiplexed serial data bus 206 controlled by an on-board vehiclecomputer 208 having an RS-485 interface 210. Preferably, a centraldisplay unit 212 is connected either directly to the computer 208 or isoperatively connected (as shown) to the computer 208 via the data bus206.

The serial data bus 206 is suitably an 18-gauge twisted pair ofinsulated wires (labeled “A” and “B”), preferably with a minimum of onetwist per inch, with an overall length of less than 40 meters. It iswithin the scope of the invention that if no data bus is provided on thevehicle, one can be added thereto. For example, in the absence of anexisting vehicle data bus, a dedicated data bus may be provided, such asa bi-directional data bus conforming to RS-485 or other suitable serialcommunications standards.

Each of the four tires 204 a . . . 204 d is equipped with an electronicmodule (“TAG”) 220 a . . . 220 d, respectively, and associated sensor(not shown, well known) capable of monitoring one or more conditionssuch as air pressure and air temperature within the tire, andtransmitting a radio frequency (RF) signal indicative of (e.g.,modulated as a function of) the monitored condition(s) within therespective vehicle tire. The tags 220 a . . . 220 d are suitablytransponders, but may alternatively simply comprise one or morecondition sensors and a radio frequency transmitter. The tags 220 a . .. 220 d are described in greater detail with respect to FIGS. 3 and 3A,herein below.

The system 200 comprises four LPWS wheel station readers (monitors) 230a . . . 230 d, each associated with a respective one of the tires 204 a. . . 204 d and located in close proximity therewith, such as mountedwithin the wheel wells of the vehicle. Each monitor 230 a . . . 230 dcomprises an antenna 232 a . . . 232 d, respectively, which is attachedat a fixed position on the vehicle adjacent the tire, within the nearfield of the respective tag (220). As mentioned herein above, the use ofnear field transmission has many distinct advantages over transmittingover an inherently greater distance from each wheel to a centrallocation on the vehicle.

Each monitor (230) is connected to a source of power (as indicated bythe lines terminating in circles and triangles) and is connected to themultiplexed serial data bus 206 for individually communicating with theon-board computer 208. The monitors 230 a . . . 230 d are described ingreater detail with respect to FIG. 4, hereinbelow.

Each monitor 230 a . . . 230 d is generally comparable to aninterrogator of a conventional transponder system, in that it comprisesan antenna 232 a . . . 232 d, a receiver (not shown) for receivingtransmissions for the tag, and a transmitter (not shown) fortransmitting signals (and optionally power) to a respective one of thetags 220 a . . . 220 d. Each antenna 232 a . . . 232 d couples with anassociated one of the tags 220 a . . . 220 d, respectively.

It is within the scope of the invention that all components of themonitor (230), including the antenna (232) can be encapsulated in asingle package. Alternatively, the antenna (232) can be deposed outsideof each a package. The antenna 232 is suitably a coil of wire on aferrite rod, such as is described in the aforementioned U.S. Pat. No.4,220,907 and U.S. Pat. No. 4,319,220.

Each monitor 230 a . . . 230 d comprises a suitable data transceivers(such as the DS36277 Dominant Mode Multipoint Transceiver by NationalSemiconductor), discussed in greater detail hereinbelow, to facilitatetwo-way data transmission via the data bus 206.

In this manner, monitored condition information carried by the RFsignals from the respective tags (220) can be decoded (e.g.,demodulated) and provided to the on-board computer 208 for subsequentdisplay (212) to the operator of the vehicle. It is within the scope ofthe invention that suitable discernable visual and/or audible warningscan be used at the option of the vehicle manufacturer.

A monitor's transmissions to the respective tag may comprise a carriersignal for energizing a passive tag, and may comprise signals to “wakeup” an active tag which is in a low-power sleep mode.

Monitored condition information carried by the RF signals from therespective tags 220 a . . . 220 d can be decoded (e.g., demodulated) andprovided to the on-board computer 208 for subsequent display (212) tothe operator of the vehicle 202. It is within the scope of the inventionthat suitable discernable visual and/or audible warnings can be used atthe option of the vehicle manufacturer.

Regarding communications occurring over the serial data bus 206,multiplex (MUX) wiring, or networking, is generally well known, and hasbeen introduced in automotive applications to address the increase incomplexity and the number of onboard electronic devices in automobiles.

For example, the Society of Automotive Engineers (SAE) has promulgatedthe J1708 “Recommended Practice” for implementing a bi-directionalserial communications link, defining parameters of the serial link thatrelate primarily to hardware and basic software compatibility such asinterface requirements, system protocol, and message format. J1708 is ahardware and basic communications protocol specification. Theaforementioned DS36277 is a transceiver based on a standard RS-485transceiver and optimized for use with J1708. The physical media of theJ1708 serial data bus is 18-gauge twisted pair with a minimum of onetwist per inch, with a maximum intended length of 40 meters. A follow-upto J1708 is the SAE J1587 Recommended Practice which defines a formatfor messages and data being communicated over the J1708 data bus. Anumber of message identification numbers (MIDs) are assigned totransmitter categories, and no two transmitters in the system shall havethe same MID. Subsystem identification numbers (SIDs) are assigned,there being a plurality of SIDs definable for each MID. For example,there are a number of engine SIDs, a number of transmission SIDs, etc. Anumber of parameter identification characters (PID) are assigned.

For example, PID “241” is assigned to tire pressure, and PID “242” isassigned to tire temperature.

AN EXEMPLARY TIRE TAG

FIG. 3 is a simplified schematic illustration of an exemplary tag 300(compare 220 a . . . 220 d) for use in the system 200 of FIG. 2. The tag300 is preferably a transponder, and comprises an antenna 302, areceiver 304, a transmitter 306, a pressure sensor 308, a temperaturesensor 310, signal conditioning circuitry 312, and a microcontroller 314which may preferably have a unique identification (ID) number associatedtherewith, the aforementioned electronic components being interconnectedas shown in the figure.

The tag (transponder) 300 is an electronic device that requires power tooperate, and may be either “active” or “passive”. As mentionedhereinabove, “passive” transponders are transponders powered by theenergy of a signal received from an external “interrogator” apparatus.“Active” transponders are transponders having their own power supply(e.g., a battery). FIG. 3 illustrates a passive version of the tag 300,wherein a power supply 320 rectifies an RF signal received on theantenna 302 and provides a raw DC signal to a power supply circuit 320(typically comprising a bridge rectifier and a storage capacitor), whichsupplies DC current to an optional power regulator circuit 322 forpowering the other components of the tag 300. The components of the tag300 are suitably disposed within a package 324 to protect thecomponents. The package 324 is suitably a plastic package within whichthe components are encapsulated. The antenna 302 is shown as beingdisposed within the package 324. However, it should be understood thatthe antenna 302 could be disposed outside of the package 324 including,for example, a loop of wire extending about the circumference of thetire on an inside surface thereof.

FIG. 3A illustrates an active version of the tag 300 a (compare 300),wherein a battery 330 provides power to a power supply circuit 320 a(compare 220) to a power regulator 322 a (compare 322) to power theother components of the tag 300 a. The battery 330 is suitably locatedoutside (as shown) of the package 324.

AN EXEMPLARY LPWS MONITOR

As mentioned hereinabove, monitors (230 a . . . 230 d) are attached tothe vehicle and located adjacent to each tire (204 a . . . 204 d) suchthat a low-powered radio transmission can take place between the tireand the respective monitor in a controlled manner. The LPWS monitorcomprises a transmitter to address the tag within the tire, a receiverto receive pressure (and, optionally, temperature) data from the tag(220 a . . . 220 d) within the tire, and a controller to supervise thesequencing of transmitter/receiver operation and to transmit datareceived from the tag over the vehicle data bus (106).

FIG. 4 is a simplified schematic illustration of an exemplary monitor400 (compare 230) for use in the system 200 of FIG. 2 with atransponder-type tag such as was described with respect to FIGS. 3 and3A.

The monitor 400 comprises an antenna 402 (compare 232), a receiver 404for receiving transmissions from the tag (300), a transmitter 406 fortransmitting to the tag (300), and a controller 408 for controlling theoperation of the monitor 400. The transmissions to the tag may comprisea carrier signal for energizing a passive tag, and may comprise signalsto “wake up” an active tag which is in a low-power sleep mode. These,and other components of the monitor 400 are suitably disposed within apackage 410 to protect the components. The package 310 is suitably aplastic package within which the components are encapsulated. Theantenna 402 is shown as being disposed outside of the package 410.However, it should be understood that the antenna could be disposedwithin the package 410.

The monitor 400 is preferably hard-wired, via a power regulator 412which is preferably contained within the package 410, to the automobilepower (vehicle power supply), typically positive 12 volts (“+12 V”) andground (“GND”).

The monitor 400 also comprises a data transceiver 420 which ispreferably contained within the package 410. The data transceiver 420 isoperatively connected to the controller 408, as illustrated tofacilitate two-way data transmission between the controller 408 and avehicle data bus 430 (compare 206). The vehicle data bus 430 is suitablybi-directional and conforms to RS-485 communications standards.

As mentioned hereinabove, if no data bus is provided on the vehicle, onecan be added thereto. For example, in the absence of an existing vehicledata bus (206), a dedicated data bus may be provided, such as abi-directional data bus conforming to RS-485 or other suitable serialcommunications standards.

The data transceiver 420 is suitably a DS36277 Dorninant Mode MultipointTransceiver, by National Semiconductor. The DS36277 Dominant ModeMultipoint Transceiver is designed for use on bi-directionaldifferential busses. It is optimal for use on Interfaces that utilizeSociety of Automotive Engineers (SAE) J1708 Electrical Standard. Thedevice is similar to standard TIA/EIA-485 transceivers, but differs inenabling scheme. The Driver's Input is normally externally tied LOW,thus providing only two states: Active (LOW), or Disabled (OFF). Whenthe driver is active, the dominant mode is LOW, conversely, when thedriver is disabled, the bus is pulled HIGH by external bias resistors.The receiver provides a FAILSAFE feature that guarantees a known outputstate when the Interface is in the following conditions: Floating Line,Idle Line (no active drivers), and Line Fault Conditions (open orshort). The receiver output is HIGH for the following conditions: OpenInputs, Terminated Inputs (50 Ohm), or Shorted Inputs. FAILSAFE is ahighly desirable feature when the transceivers are used withAsynchronous Controllers such as UARTs.

Although the invention has been illustrated and described in detail inthe drawings and foregoing description, the same is to be considered asillustrative and not restrictive in character it being understood thatonly preferred embodiments have been shown and described, and that allchanges and modifications that come within the spirit of the inventionare desired to be protected. Undoubtedly, many other “variations” on the“themes” set forth hereinabove will occur to one having ordinary skillin the art to which the present invention most nearly pertains, and suchvariations are intended to be within the scope of the invention, asdisclosed herein.

What is claimed:
 1. In a vehicle having pneumatic tires, a system formonitoring tire pressure comprising an RF tag associated with each ofthe vehicle tires, each tag providing a signal indicative of respectivetire pressure; the system characterized by: a monitor associated witheach of the RF tags, each monitor being mounted in close proximity witheach respective tire; one central computer; and a bi-directional serialdata bus connected to the computer and to each of the monitors.
 2. Thesystem of claim 1, characterized in that: the RF tag is a transmitter.3. The system of claim 1, characterized in that: the RF tag is atransponder.
 4. The system of claim 3, characterized in that: the RF tagis a passive transponder.
 5. The system of claim 3, characterized inthat: the RF tag is an active transponder.
 6. The system of claim 1,characterized in that each monitor comprises: a ferrite rod antenna forcoupling with an associated one of the RF tags.
 7. The system of claim1, characterized in that: the data bus comprises a vehicle data bus, foruse in multiple vehicle data communication tasks.
 8. The system of claim1, characterized by: a display connected to the data bus.
 9. The systemof claim 1, characterized in that: the data bus comprises a dedicateddata bus, for exclusive use with the system for monitoring tirepressure.
 10. The system of claim 1, characterized in that: the data busconforms to RS-485.
 11. The system of claim 1, characterized in that:the RF tag provides a signal indicative of respective tire temperature.12. A method of monitoring vehicle tire pressure wherein the RF tag isassociated with each of the vehicle tires, each tag providing a signalindicative of respective tire pressure; the method characterized by thesteps of: mounting a monitor in close proximity to each tire such thateach monitor communicates with the RF tag associated with the respectivetire; using each monitor for converting between RF signals and datastreams suitable for a bi-directional serial data bus; connecting themonitors and a single on board computer to the data bus; and using thecomputer for interpreting and displaying data form the RF tags.
 13. Themethod of claim 12, characterized in that: the RF tag is a transmitter.14. The method of claim 12, characterized in that: the RF tag is atransponder.
 15. The method of claim 14, characterized in that: the RFtag is a passive transponder.
 16. The method of claim 12, characterizedby: comprising each monitor of a ferrite rod antenna for coupling withan associated one of the RF tags.
 17. The method of claim 12,characterized by: conforming the data bus to RS-485.
 18. The method ofclaim 12, characterized by: sharing the data bus as a vehicle data bus,for use in multiple vehicle data communication tasks.
 19. The method ofclaim 12, characterized by: dedicating the data bus to exclusive usewith the system for monitoring tire pressure.
 20. The method of claim12, characterized by: measuring tire temperature with the RF tag.